I've worked in startups long enough to see many founders build without considering ROI.

It's not rare at all.

The reason you don't see those projects is because they don't make it very far. Big projects take a lot of effort and people and most people expect compensation for their effort. You can't compensate them without ROI.

As an open-source project they have some benefit of getting contributors to do some of the work. The hardware still needs ROI to exist. Making those custom parts requires up-front capital, which is going to need ROI to pay back.